Process for preparation of diffusion barrier for semiconductor

ABSTRACT

A process for preparing a diffusion barrier on a semiconductor substrate which comprises: conducting remote plasma-enhanced metal organic chemical vapor deposition of a thin film of TiNx on said substrate using an organotitanium compound under a flow of H2 plasma, wherein x ranges from 0.1 to 1.5, provides a TiNx thin film having a low carbon content and low specific resistivity.

FIELD OF THE INVENTION

The present invention relates to a process for preparing a diffusionbarrier for a semiconductor device; and more particularly, to a processfor preparing a diffusion barrier having a low specific resistivity on asemiconductor substrate by way of conducting remote plasma-enhancedmetal organic chemical vapor deposition of a thin film of TiN_(x) undera flow of H₂ plasma as a reaction gas.

BACKGROUND OF THE INVENTION

Recently, TiN_(x) has drawn attention as an important material for ultralarge scale integrated circuits (ULSIC) having a line width of 0.5pm orless; a TiN_(x) thin film is used as a diffusion barrier to protectshallow silicon junctions in the formation of Al contacts on a siliconwafer (J-Y Yun and S- W Rhee, Korean J. Chem. Eng., 13(5), 510(1996)).

Such diffusion barrier is required to have a low specific resistivityamong others, and the specific resistivity of a TiN_(x) film isinfluenced by the presence of impurities such as carbon and oxygen,structural defects such as vacancies, and also by the size of the grainsthat constitute the film. The grain size varies with the processconditions such as the deposition temperature, and in general, as thegrain size becomes larger, the specific resistivity of the film becomeslower. It is particularly important to minimize impurity content of aTiN_(x) film if it is intended for use as a diffusion barrier.

Chemical vapor deposition(CVD) has been widely used in the preparationof TiN_(x) films, wherein inorganic compounds such as titaniumtetrachloride (TiCl₄) or organotitanium compounds such astetrakis-dimethylamidotitanium (TDMAT) andtetrakis-diethylamidotitanium(TDEAT) are generally employed asprecursors (I. J. Raaijmakers, Thin Solid Films, 247, 85(1994); S. R.Kurtz and R. G. Gordon, Thin Solid Films, 140, 277(1986))).

CVD of TiN_(x) using TiC₄ is disadvantageous in that the depositiontemperature ranging from 500 to 600 C is generally too high for theULSIC application, and also that chlorine may be incorporated in thefinal TiN_(x) film, causing a corrosion problem (I. J. Raaijmakers, lococitato).

Further, CVD of TiN_(x) using organotitanium compounds often entailsproblems such as carbon contamination, a low step coverage and highspecific resistivity. For example, when a TiN_(x) film is deposited by aCVD process using an organotitanium compound in the presence of gaseousammonia as a reaction gas, ammonia reacts with the precursor in the gasphase to form particles. The particles thus formed get incorporated intothe TiN_(x) film and the smoothness of the film surface becomesdeteriorated, leading to an increase in the specific resistivity (J. A.Prybyla et al., J. Electrochem. Soc., 140, 2695(1993)).

To avoid such problems, a thermal decomposition process which uses anorganometallic compounds in the absence of ammonia has been suggested.However, this process gives a high level of contaminants and theresulting film has a high specific resistivity (I. J. Raaijmakers, lococitato).

SUMMARY OF THE INVENTION

It is, therefore, a primary object of the present invention to provide aprocess for the preparation of a TiN_(x) diffusion barrier for asemiconductor device, said TiN_(x) barrier having a low carbon contentand low resistivity.

In accordance with the present invention, there is provided a processfor preparing a diffusion barrier on a semiconductor substrate whichcomprises: conducting remote plasma-enhanced metal organic chemicalvapor deposition of a thin film of TiN_(x) on said substrate using anorganotitanium compound under a flow of H₂ plasma, wherein x ranges from0.1 to 1.5.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the present invention willbecome apparent from the following description of the invention, whentaken in conjunction with the accompanying drawings, in which:

FIG. 1 shows a schematic diagram of an apparatus for the remoteplasma-enhanced metal organic chemical vapor deposition used inpracticing one embodiment of the present invention;

FIGS. 2A and 2B depict X-ray photoelectron spectroscopic scans ofTiN_(x) thin films prepared by the plasma chemical vapor depositionmethod (2A: H₂ plasma, 2B: N₂ plasma); and

FIG. 3 demonstrates the variation of the specific resistivity of theTiN_(x) film as a function of the flow rate of the gaseous plasma.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the term “a TiN_(x) thin film” means a thin filmcontaining titanium and nitrogen in a ratio ranging from 0.1 to 1.5.

The representative substrates, which may be used in the presentinvention, include semiconductor devices such as D-RAM, S-RAM, F-RAM,Logic, AISIC, microprocessor and TFT.

The representative organotitanium precursors, which may be used in thepresent invention, include alkylamidotitanium derivatives such as TDMATand TDEAT.

Generally, such alkylamidotitanium compound undergoes thermaldecomposition to form a ring compound containing a three-membered Ti-N-Cring by p-hydrogen elimination as in Eq. (1).

In a thermal chemical vapor deposition process using the above organicprecursor in the absence of a reaction gas, the ring compound may beincorporated into the TiN_(x) film produced, and thus, the final filmtends to contain a large amount of carbon, i.e., 20 to 30%.

In case when N₂ plasma is used in a CVD process, a similar thermaldecomposition reaction of the precursor apparently takes place, asjudged from the observation that a major amount of carbonaceous carbonis incorporated into the TiN_(x) film formed.

In contrast, when H₂ plasma is employed in a CVD process, hydrogenradical species generated in the H₂ plasma react with the precursor toform a Ti-rich TiN_(x) and a stable alkylamine as a byproduct whichescapes from the reactor without leading to a carbonaceous material.Accordingly, only a small amount of carbon is incorporated into theTiN_(x) film and the specific resistivity of the final film is lowerthan that prepared by using N₂ plasma CVD.

Thus, the H₂ plasma-enhanced CVD process of the present inventionprovides a TiN_(x) film having a low specific resistivity due to its lowcarbon content of less than 30 atom % based on the sum of titanium,nitrogen and carbon atom constituents of the film.

The thin film of TiN_(x) of the present invention may be formed as adiffusion barrier for a semiconductor device in accordance with theprocess described below:

FIG. 1 shows a schematic diagram of an apparatus for the remoteplasma-enhanced metal organic chemical vapor deposition process of thepresent invention, which comprises a feeding system for anorganotitanium compound, a chemical vapor deposition reactor, and avacuum system which controls the pressure within the reactor. A reactiongas(1) is delivered to an upstream region of the reactor, i.e., plasmagenerating region, and then, is excited by plasma generator(4) (electricpower: 1-80W; temperature: 250-500° C.; flow rate of plasma reactiongas: 20-150 sccm); while the organometallic compound(2) and carriergas(3) are delivered from the bubbler to a downstream region of thereactor.

The excited reaction gas (1) reacts with the organometallic compound (2)to produce a TiN_(x) thin film on the substrate (7) wherein thetemperature of the substrate is adjusted by temperature controller (5)and the total pressure in the reactor was controlled at a presetpressure, e.g., 1 Torr, using diffusion pump (6).

The following Example are intended to illustrate the present inventionmore specifically, without limiting the scope of the invention.

In Example and Comparative Example, characterization of film samples wasconducted by employing X-ray photoelectron spectroscopy(XPS) andspecific resistivity measurement with a four point probe.

EXAMPLE

Remote plasma MOCVD of a TiN_(x) film was carried out in a cold walltype plasma chemical vapor deposition apparatus (Korea Vacuum Co.),wherein only the substrate is heated so as to prevent TiN_(x) depositiononto the wall, and the deposition was conducted using a P-type Si-(100)wafer as a substrate, TDEAT, H₂ as a plasma gas and nitrogen as acarrier gas of TDEAT.

The electric power and temperature of the plasma were 40 W and 350° C.,respectively, and the H₂ flow rate was in the range of 30 and 90 sccm,while maintaining the total pressure at 1 Torr.

The chemical constitution of the prepared TiN_(x) film was analyzed byXPS and the results are shown in Table I.

COMPARATIVE EXAMPLE

The procedure of Example was repeated except that N₂ plasma was used inplace of H₂ plasma.

The chemical constitution of the TiN_(x) film thus prepared was analyzedby XPS and the results are shown in Table I.

TABLE I Ti(atm, %) N(atm, %) C(atm, %) 30 90 30 90 30 90 sccm sccm sccmsccm sccm sccm Example 71 82 8 9 21 9 Comparative 30 46 16 11 54 43Example

As shown in Table I, the amount of carbon incorporated in the TiN_(x)thin film prepared in Example using H₂ plasma is much less than thatprepared in Comparative Example using N₂. As the flow rate of hydrogenincreases, the amount of the incorporated carbon tends to decrease. Forexample, Ti/C ratio at 30 sccm was 3.3 while that at 90 sccm was 9.1.

Further, the amount of nitrogen found in the TiN_(x) film of Example isalso less than that of Comparative Example. This result suggests that aTi-rich thin film can be prepared in accordance with the preventinvention.

FIGS. 2A and 2B depict X-ray photoelectron spectroscopic scans ofTiN_(x) thin films prepared by the plasma-enhanced chemical vapordeposition method (2A: H₂ plasma, 2B: N₂ plasma). Carbon is incorporatedinto the TiN_(x) film in the form of TiC (282 eV) or carbonaceous carbon(285 eV). It is reported that a film having TiC has a lower specificresistivity than a film having incorporated carbonaceous carbon. Asshown in FIG. 2, TiC/carbonaceous carbon ratio observed for the film ofExample is much greater than that of Comparative Example.

These results show that the amount of carbon incorporated in thediffusion barrier prepared by employing remote MOCVD with using H₂plasma in accordance with the present invention is much less than thatprepared by using N₂ plasma and the incorporated carbon exists mostly inthe form of TiC.

FIG. 3 demonstrates the variation of the specific resistivity of theTiN_(x) film as function of the flow rate of the plasma reaction gas.The specific resistivity of the TiN_(x) film prepared by using H₂ plasmais lower than that prepared by using N₂ plasma.

As shown above, a diffusion barrier for a semiconductor device having alow carbon content and low specific resistivity can be prepared byemploying the process of the present invention.

While the invention has been described with respect to the specificembodiments, it should be recognized that various modifications andchanges may be made by those skilled in the art to the invention whichalso fall within the scope of the invention as defined by the appendedclaims.

What is claimed is:
 1. A process for preparing a diffusion barrier on asemiconductor substrate which comprises: conducting remoteplasma-enhanced metal organic chemical vapor deposition of a thin filmof TiN_(x) on said substrate using an organotitanium compound under aflow of H₂ plasma, wherein x ranges from 0.1 to 1.5.
 2. The process ofclaim 1, wherein the thin film of TiN has a carbon content of less than30 atom % based on the sum of titanium, nitrogen and carbon constituentsof the film.
 3. The process of claim 1, wherein the organotitaniumcompound is tetrakis-dimethylamidotitanium ortetrakis-diethylamidotitanium.
 4. The process of claim 1, wherein thesemiconductor substrate is a silicone wafer.